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Casein kinase I Does Not Rescue double-time Function in Drosophila Despite Evolutionarily Conserved Roles in the Circadian Clock

Division of Insect Sciences, National Institute of Agrobiological Sciences, Ohwashi 1-2, Tsukuba, Ibaraki 305-8634, Japan, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan

Terumi Yamaguchi

Division of Insect Sciences, National Institute of Agrobiological Sciences, Ohwashi 1-2, Tsukuba, Ibaraki 305-8634, Japan

Kunikatsu Hamano

Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan

Michael W. Young

Laboratory of Genetics, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA

Masami Shimoda

Division of Insect Sciences, National Institute of Agrobiological Sciences, Ohwashi 1-2, Tsukuba, Ibaraki 305-8634, Japan, shimoda1{at}affrc.go.jp

Lino Saez

Laboratory of Genetics, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA, saez{at}rockefeller.edu

double-time (dbt) is a casein kinase gene involved in cell survival, proliferation, and circadian rhythms in the fruit fly, Drosophila melanogaster. Genetic and biochemical studies have shown that dbt and its mammalian ortholog casein kinase I (hckI) regulate the circadian phosphorylation of period (per), thus controlling per subcellular localization and stability. Mutations in these kinases can shorten the circadian period in both mammals and Drosophila. Since similar activities in circadian clock have been described for these kinases, we investigated whether the expression of mammalian casein kinase I can replace the activity of dbt in flies. Global expression of the full-length dbt rescued lethality of the null mutant dbt ^revVIII and rescued flies showed normal locomotor activity rhythms. Global expression of dbt also restored the locomotor activity rhythm of the arrhythmic genotype, dbt^ar/dbt^revVIII. In contrast, global expression of hckI or hckI did not rescue lethality or locomotor activity of dbt mutants. Furthermore dbt overexpression in wild-type clock cells had only a small effect on period length, whereas hckI expression in clock cells greatly lengthened period to ~30.5 hours and increased the number of arrhythmic flies. These results indicate that hckI cannot replace the activity of dbt in flies despite the high degree of similarity in primary sequence and kinase function. Moreover, expression of hckI in flies appears to interfere with dbt activity. Thus, caution should be used in interpreting assays that measure activity of mammalian casein kinase mutants in Drosophila, or that employ vertebrate CKI in studies of dPER phosphorylations.

Key Words: circadian • casein kinase • locomotor activity

Journal of Biological Rhythms, Vol. 23, No. 1, 3-15 (2008)
DOI: 10.1177/0748730407311652


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